1. Technical Field
The present invention relates to a matrix-type display apparatus which drives a plurality of pixels disposed in matrix form and displays an image, and its driving method.
2. Background Art
In a liquid-crystal display apparatus where a TN (or twisted nematic) system is used, a liquid crystal has a refractive-index anisotropy, a twist orientation, or the like. Thus, a beam of light which passes through a liquid-crystal layer is subjected to various birefringence effects, depending upon its direction or angle. This allows a complicated visual-angle dependence to appear. For example, the whole screen image becomes whitish at an upper visual angle while the entire screen image becomes dark at a lower visual angle. Besides, light and shade are reversed within an image's low-luminance range. In terms of these visual-angle characteristics, various techniques have been developed for widening a viewing angle about a luminance, a hue, a contrast characteristic, a gradation characteristic, or the like.
For example, Japanese Patent Laid-Open No. 5-68221 specification discloses a liquid-crystal display apparatus. If the number of times at which a signal is written in one pixel for a one-field period is n, then n+1 levels are driven using only two black and white values. The other levels are driven using a combination of a gray level and white or black level. Thereby, a γ-characteristic (i.e., a transmittance characteristic according to an input level) is changed.
In addition, another liquid-crystal display apparatus is disclosed in Japanese Patent Laid-Open No. 9-90910 specification. A plurality of applied voltages which are generated by a plurality of conversion methods of converting input signals at the same level into different applied voltages are selectively applied for each pixel. Thereby, two different types of γ-characteristics are switched so that the distribution area ratios are identical.
However, in the former liquid-crystal display apparatus, two black and white values are used only in the case where the transmittance to be used for display is 50 percent. Then, a combination of a gray level and white or black level is used in the case of the other transmittances. Hence, a viewing angle characteristic can be improved at a transmittance of 50 percent. However, at a transmittance other than this, for example, at 25 percent or 75 percent, if a viewing angle is deflected, a γ-characteristic after synthesized deviates largely from an intrinsic γ-characteristic. This makes it impossible to realize a good viewing angle characteristic at a wide-ranging transmittance.
Furthermore, in the latter liquid-crystal display apparatus, a synthetic γ-characteristic is used which is obtained through a synthesis after two types of γ-characteristics are changed so that the distribution area ratios are the same. Therefore, if a viewing angle is deflected, then in accordance with a transmittance, a γ-characteristic after synthesized deviates largely from an intrinsic γ-characteristic. Even in this case, a good viewing angle characteristic cannot be realized at a wide-ranging transmittance.